Field of the Invention--This invention relates to a process for the preparation of cyano-substituted carboxylic acid esters by reacting an acid anhydride, an aromatic aldehyde and a water-soluble cyanide.
Description of the Prior Art--A valuable group of esters consists of pesticides of the pyrethrin type, particularly those .alpha.-cyano esters as described, for example, in U.S. Pat. Nos. 3,835,176, 3,996,244 and 4,024,163. These so-called "synthetic pyrethroids" have exceptionally good insecticidal and acaricidal properties while possessing a very low mammalian toxicity. This combination of properties makes these .alpha.-cyano esters of considerable interest to the agrochemical industry and much effort has ben devoted to finding economic routes to these "synthetic pyrethroids".
Belgian Pat. No. 851,900 discloses the preparation of cyano-substituted esters from an acid halide, an aldehyde and a water-soluble cyanide.
The process of the present invention based upon the use of an acid anhydride affords the .alpha.-cyano esters in a very high yield.